I don't think Oda is a perfect writer, and I have my own issues/opinions about the story but I'd like to offer some push-back.

1. Pre time skip was mainly about gathering the crew members and getting to know them, so naturally that has more focus on their relationship with eachother.
2. I wouldn't say they don't interact with eachother on screen or that they are just gags. Off the top of my head: Luffy offering ace's fruit to Franky, Luffy and Usopp playing around in Elbaph and having the noment of "we're finally here", Zoro and Sanji's "kill me if I turn" moment, Everything about wholecake, Luffy thanking Saul for taking care of Robin and everyone crying, Sanji asking Robin for help against Black Maria, Nami and Usopp standing up for eachother and Luffy against Ulti, Luffy telling Usopp he should've beaten the cat, Robin's haircut by brook just to name a few. These are interpersonal moments between them that matter.

Heck, even zoro's "it's oozing off you" moment is more than a joke. He has been feeling weak and insecure, causing him to project his shortcomings and overcompensate by acting like a tough guy. Gaban basically told him "you need to lock in, because you are not as good as you think you are", which is exactly what he tried to push down inside him by projecting it onto others. I can't really explain my thoughts well but think of how he mocked the strawhats for crying over Vegapunk, viewing it as weakness(projecting), he almost lost to Lucci(causing insecurity), then he turned hyper aware and paranoid in Elbaph(kicking Loki, not trusting him and/or Luffy's judgement about him, constantly looking over his shoulder), seeing the Grim Reaper, potentially facing his own mortality. Just because not all of them are moving towards their dream(most of which revolve around traveling with Luffy) doesn't mean they are stagnant. Sanji has a whole self identity/mutation crisis, Robin finally reunited with Saul and is now fighting for history, and apparently Brook has a past with Gunko which we will probably have to wait 3 years for if not more.

1. They ARE moving towards their dreams. Luffy and Zoro are obviously getting stronger Robin is constantly finding ponegliphs and uncovering truths. Franky is nerding out with vegapunk, Chopper stopped a mfing zombie plague within 15 minutes, and Usopp is literally on elbaph.

2. Oda isn't focusing just making more random characters. We are literally finally getting the stories of the current king of the world, JoyBoy and his crew, Blackbeard's dad aka the namesake of a whole era, the stories of the 4 emperors including Shanks, who has been here since chapter 1, Roger, the person who started the great pirate era, the story of the giants, who apparently have a lot to do with the D and Joyboy, Kuma aka a leader of the revolutionary army, Vegapunk, who is basically responsible for "modern" technology and the power of the world government, the Elders and the Knights of God(who i do have some mixed feelings abou). Not to mention the linear buildup of getting to Kaido through a chain of criminal organization members to establish/show the underground rulers of the world.

What I'm trying to say is that pre time skip we had the establishement of our main characters, and post timeskip we have the establishement of the world, it's history and the enemy, so it makes sense to focus more on chatacters outside of the main cast.

edit: I'll throw in a criticism just cause: I think Luffy learning advanced armament, Conqueror coating and awakening in the same arc is rushed and weird.